A story of unintended consequences: lessons for the Mekong Delta

Thu, 02 Aug 2012

At a meeting of foreign ministers in Phnom Penh, Cambodia on July 13, 2012, U.S. Secretary of State Hillary Clinton stated: "I'll be very honest with you. We made a lot of mistakes. We've learned some hard lessons about what happens when you make certain infrastructure decisions and I think that we all can contribute to helping the nations of the Mekong region avoid the mistakes that we and others made."

Mrs. Clinton was speaking from long experience. In 1850, the U.S. Congress passed the Swamp and Overflowed Land Act. At the time, the law made sense: transfer federally-owned wetlands to the states so they could drain and dike them to make the land suitable for cultivation. Congress also granted federally owned wetlands to the State of Louisiana “ostensibly to help control flooding in the Mississippi River Valley.” In retrospect, we now know that what the states and Congress failed to take into account is that wetlands control and attenuate floods without the need for costly man-made engineering. In fact, nature does the job so well that all we need to do is to leave it alone.

In 1879, Congress created the Mississippi River Commission to manage federal funds for flood control projects along the Mississippi. The Commission decided that the best way to control the river was to line its banks with levees (dikes). In 1927, the Mississippi broke its banks and killed 246 people in seven states. It was the most destructive river flood in the history of the U.S. In response, the Army Corps of Engineers built the world’s longest system of levees along the Mississippi. The Corps also drained the river’s wetlands and converted them to agriculture. Hydrologically speaking, the Mississippi was now cut off from its floodplains. The floodplains, which once served to absorb floods, filter water and sediment, and provide habitat for native plants and animals, now serve only the inhabitants of the cities and intensive farms that have built upon them.

The costs of this approach are now apparent. The levees and dams on the Mississippi have restricted the supply of sediment to the delta, which is now shrinking rapidly. In 2005, the loss of coastal wetlands exposed New Orleans to the full force of Hurricane Katrina, the costliest natural disaster in the history of the U.S. More than 1,800 people died in the actual hurricane and in the subsequent floods, and total property damage was estimated at $81 billion. To prevent similar flooding, the Army Corps of Engineers designed a coastal protection system based on bigger dikes with an annual maintenance cost of $150 million. Louisiana, which by law has to prepare a balanced budget, could not afford this expense and is now pursuing a policy of “strategic retreat” by withdrawing all public services (schools, water and electricity supply, etc.) south of Interstate-10, the highway that runs east-west through New Orleans..

What can the Mekong Delta learn from the Mississippi Delta? The most important lesson is that re-engineering the delta’s hydrology has unexpected consequences. This is already evident. For example, the canals that were cut through Kien Giang to connect An Giang to the Gulf of Thailand to support increased rice production have resulted in the rapid loss of mangroves because the canals disturbed the along-shore mud supply. Mangrove loss has exposed sea dikes to wave action, which has led to dike collapse and coastal flooding. Another example is the construction of high dikes in An Giang, Dong Thap, and Long An to support a third (or fourth) rice crop. This has shrunk the floodplain, constricted the river flow, and flooded urban and industrial areas downstream. Finally, the conversion of the Plain of Reeds from a vast natural sponge, which absorbed water in the wet season and slowly released it the dry season, to intensive rice production has reduced river base flows and allowed salt water to penetrate further upstream during the dry season.

The government is currently considering the construction of a 28 km-long sea dike connecting Vung Tau and Go Cong combined with a sluice gate on the Vam Co River. The purpose is to prevent flooding of HCMC, reduce saline intrusion, and increase the area in the Plain of Reeds under three rice crops. The cost is estimated at $2.8 billion (which global experience suggests could be 25% of the actual cost). A report on the sea dike by several state water research institutions had very little to say about the environmental costs except that: “adverse impacts of the project are less than impacts of alternative solutions and the negative impacts can be mitigated.”

A much cheaper and less risky way to reduce wet season flooding and dry season saline intrusion would be to increase the absorptive capacity of the Plain of Reeds by allowing parts of it to return to a natural or semi-natural state. As the climate warms and rainfall intensifies, the ability of wetlands to absorb flood water will become increasingly important—and a vital part of the delta’s climate change adaption strategy. A less intensively cropped Plain of Reeds would reduce rice production but increase capture fisheries, which is vital to the landless poor who make up 20% of the delta’s population. It would also allow the return of high-value traditional long-stem rice varieties. At the very least, the restoration of the Plain of Reeds could delay the need to build a massive sea dike by several decades. At a time of economic austerity, this is an attractive message for government.

Unlike the Mississippi Delta, the hydrology of the Mekong Delta remains relatively natural. There are no dams (yet) on the Lower Mekong to trap large volumes of sediment and the dikes that have been built are permeable and prone to collapse. Before making expensive and irreversible investment decisions (such as the Vung Tau-Go Cong sea dike), the government has the opportunity (and, given the risks involved, the duty) to learn from international experience. As in the U.S., there are powerful vested interests in favor of big engineering projects. For these groups the answer is always the same: “pour more concrete.” But whereas the benefits of this approach are captured by a few, the costs are borne by the many long after construction is complete. Fortunately, our scientific understanding of how deltas function is infinitely greater than it was in 1850 and, as Mrs. Clinton stated clearly, there is no need to repeat the mistakes of the past.